1. Field of the Invention
The present invention relates to a system for detecting the location where a material handling vehicle currently is in a warehouse in which a plurality of racks composed of upright frame members and lateral frame members connecting the upright members are installed so that material handling vehicles such as forklift trucks can travel between the racks.
2. Description of the Related Art
There has been known systems for detecting the actual location of a material handling vehicle operating material handling in a warehouse, in which the actual position of the vehicle is determined from image data of a photograph taken by a camera attached on the vehicle through pattern matching process or from a light beam or radio waves reflected from reflector plates located at predetermined positions by emitting a light beam or radio waves from a rotating projector attached on the vehicle.
In Japanese Patent No. 3443829 (patent literature 1) is disclosed a location detecting system, in which a laser navigator 8 is provided at an arm top part 7 of a forklift truck 2, and reflector plates 16 are adhered to shelves 14 at a height position about the same as that of the laser navigator 8. The location of each of the reflector plates is memorized in an on-vehicle controller 10. The laser navigator 8 emits a laser beam to allow it to scan 360° in a horizontal plane, receives reflection from the reflector plates 16. The reflection is checked with the map and actual location of the forklift truck is determined.
The height of a fork 4 is detected by an encoder connected to a guide roller 6 and the number of the shelf where material is handled is determined in combination with the detected location of the forklift truck 2 and the height position of the fork 4. Number of shelf where to handle material is directed by the controller 10. Every time material is handled according to the directive, the number of the shelf where material is handled is compared with the shelf number directed by the controller 10 to verify that material handling is performed as directed by the controller 10.
With this location detecting system, a means for allowing a laser beam to scan 360° in a horizontal plane is needed to detecting actual location of a material handling vehicle, and system structure is not so simple.
Further, it correct reading of the reflector plates fails, the controller misjudges the position of the material handling vehicle, and whether the position of the vehicle is detected correctly or not can not be checked, that is, degree of correctness of the detection of the position can not be grasped in point of view of probability theory. Therefore, with the system, management functions of material handling are still not sufficiently improved.